Methods and devices for attenuating sound in a conduit or chamber

ABSTRACT

Occlusion devices, earpiece devices and methods of forming occlusion devices are provided. An occlusion device is configured to occlude an ear canal, but other biological and non-biological conduits or chambers can be occluded using the devices and methods herein. The occlusion device includes an insertion element and at least one occluding member or element (which can be expandable) disposed on the insertion element. The occluding member is configured to receive a medium via the insertion element and is configured to expand, responsive to the medium, to contact the ear canal. Alternatively, the occluding member is made of a non-Newtonian fluid and can be enclosed by a balloon or not. Physical parameters of the occlusion device are selected to produce a predetermined sound attenuation characteristic over a frequency band. Use of a non-Newtonian fluid provides additional options or variables in customizing or designing a predetermined sound attenuation characteristic.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.16/543,605, filed 18 Aug. 2019, which is a continuation of U.S. patentapplication Ser. No. 15/168,020 filed May 28, 2016, which claims thepriority benefit of Provisional Patent Application No. 62/168,703entitled “METHODS AND DEVICES FOR ATTENUATING SOUND IN A CONDUIT ORCHAMBER” filed on May 29, 2015, the entire contents of both areincorporated herein by reference in their entirety.

FIELD

The present embodiments relate to occluding elements used forattenuating sound or isolating sound from a closed conduit or chambersuch as an ear canal.

BACKGROUND OF THE INVENTION

Non-Newtonian fluids and more particularly, shear thickening fluids arebeing considered and investigated for potential commercial use asmaterials for liquid body armour or protective clothing due to theirunique properties. The primary focus of the investigations have revolvedaround adaptive stiffness and dampening properties that can preventballistic weapons or sharp knives or stakes from penetrating a piece ofbody armour or protective clothing.

People may be exposed to noise pollution from their ambient environment(for example, from traffic, from construction sites, from aircraft,etc.). People may also be intentionally exposed to high sound levels(for example, from cell phones, MP3 players, home theater equipment,rock concerts, etc.). Studies have shown that ear damage, which may leadto permanent hearing impairment, is not only increasing in the generalpopulation, but may be increasing at a significantly faster rate inyounger populations. The potential for noise induced hearing loss (NIHL)may be a function of both a level and a duration of exposure to a soundstimulus. Studies have also indicated that hearing damage is acumulative phenomenon. Although hearing damage due to industrial orbackground noise exposure is more thoroughly understood, there may alsobe a risk of hearing damage from the exposure to intentional excessivenoise, such as with the use of headphones.

Devices which attenuate sound directly to the ear canal are known.Conventional devices typically fit in the ear, around the ear and/orbeyond the ear. Examples of these devices include headphones, headsets,earbuds and hearing aids. Earpieces that occlude the ear canal mayprovide increased attenuation of the ambient environment, offeringimproved sound isolation. However, conventional in-ear, in-concha or incanal earpieces may be fitted for a cross-section of a population andmay not provide adequate sound isolation. Conventional in-ear, in-conchaor in canal earpieces, thus, may not be properly fitted to theindividual user and may not be adequately sealed, leading to reducedsound attenuation of the ambient environment. Furthermore, even ifproperty fitted, as the ambient environment becomes louder, theeffectiveness of the existing materials used for sound attenuating orisolation in-ear earpiece (or other devices fitting outside the ear) maynot provide adequate protection. Most often, they are static in theirattenuation properties, whereby the maximum attenuation is providedregardless of the ambient sound level.

SUMMARY

The present embodiments can be embodied in a sound attenuating device,including an occluding element configured to form a closed conduit orchamber upon insertion into an open end of the conduit or chamber andthe inclusion of non-Newtonian fluid forming at least a portion of theoccluding element where the non-Newtonian fluid provides an increasing(or variable) attenuation response in response to an increasing soundpressure leveling impinging an surface exposed to the ambientenvironment of the occluding member. In some embodiments, thenon-Newtonian fluid is a shear thickening fluid or a dilatant fluid andwhere the non-Newtonian fluid includes carrier liquid and rigidcolloidal particles. In some embodiments, the non-Newtonian fluid caninclude carrier fluid selected from the group of water, ethylene glycol(EG) and the non-Newtonian fluid further includes particles,microspheres, and or microfibers selected from the group comprisingsilica, titanium, oxide, calcium carbonate, cornstarch, syntheticallyoccurring minerals, naturally occurring minerals, polymers, glass,stainless steel or a mixture of any of the aforementioned particles. Insome embodiments, the non-Newtonian fluid is a shear thickening fluidcontaining composites using rubber as a precursor and adding acatalyzing agent. In yet other variant embodiments, the first member isformed (or includes) using a shear thickening fluid combined with anopen cell polyurethane to form a foam-shear thickening fluid composite.In yet other embodiments, the non-Newtonian fluid is a non-particlebased shear thickening fluid. Examples of non-particle based shearthickening fluid can include poly vinyl alcohol containing boric acid orpoly dimethylsiloxane containing boric acid. In some embodiments, thenon-Newtonian fluid comprises anisotropic particles, sphericalparticles, or at least one of fibers, rod-like elements, nanoparticles,or nano-tubes. The non-Newtonian fluid can also be electrorheologicalfluids composed of dispersions of electrically polarizable particles inan insulating fluid that increases in shear viscosity when exposed to anelectric field. Alternatively, the non-Newtonian fluid can also bemagnetorheological fluids composed of dispersions of magnetic particlesin an inert or non-magnetic carrier liquid that increases in shearviscosity when exposed to a magnetic field. In some embodiments, thefirst member can include a balloon filled with the non-Newtonian fluid.In some embodiments, the sound attenuating device is an earpiececonfigured to occlude an ear canal with the occluding element. In someembodiments, the sound attenuating device can further include an earcanal receiver and an ear canal microphone configured to reside in asealed area when the occluding element is placed within an orifice orexternal opening of the ear canal. Note that the ear canal is just oneexample of a conduit or cavity that can be closed or occluded using themethod and devices disclosed herein. Other biological and non-biologicalconduits can equally benefit from the methods and devices disclosed orclaimed herein.

The present embodiments can also include a method of attenuating soundin a conduit or chamber. The method can include providing a open-endedconduit or chamber and forming a closed conduit or chamber using atleast a first member that includes a non-Newtonian fluid where the firstmember is placed at an open end of the conduit or chamber and where thenon-Newtonian fluid provides an increasing attenuation response inresponse to an increasing sound pressure level impinging an outersurface of the first member. The non-Newtonian fluid can include any ofthe fluids or particles or elements described above and in anycombinations or permutation thereof. Furthermore, embodiments herein canincrease the attenuation based on the ambient SPL, thus providing usersthe ability to maintain situational awareness without having to remove aprotective device (such as an earpiece or headphone) in non-hostileacoustic environments. In other words, embodiments herein maintainsituational awareness in a passive manner without the use of activecomponents or electronics. The chemistry of the non-Newtonian fluidenables a dynamic or variable attenuation characteristic that can betailored or configured by a designer with an increasing number ofvariables as explained further below. The non-Newtonian fluid canreplace or enhance conventional headset materials (such as rubber orfoam) or otherwise be incorporated into earpieces, headsets, orheadphones to enhance the attenuation efficacy of such devices based onthe ambient SPL. In other words, using non-Newtonian fluids, the greaterthe ambient SPL, the greater the attenuation properties of the earpiece,headset, earphone or earplug. This characteristic is in sharp contrastto the rubber, foam, and/or paraffin used in typical earpieces used forNIHL protection or other purposes. Non-Newtonian fluids provide forvariable attenuation, rather than a static or fixed level of attenuationexhibited by existing products. The non-Newtonian fluids provide amaximum amount of acoustic protection regardless of the acousticconditions such that the louder the acoustic conditions the greater theattenuation the earpiece (or other device using the non-Newtonian fluid)offers. The non-dynamic aspect of conventional products such as foamonly provides a static amount of attenuation.

Thus, embodiments herein using non-Newtonian fluids can providesituation awareness without the additional use of active electronics.With conventional products such as an existing foam earplug, a userwould need to remove the earplug in quiet conditions to hear ones voicein a non-hostile acoustical environment whereas the non-Newtonianembodiments herein become more acoustically transparent at low soundpressure levels (e.g., 75 dB) and increases its acoustical impendence(attenuation) as the sound pressure level above 75 dB is increased.Thus, the user in conditions where the volume is comfortable does notneed to pull the product out of their ear. The non-Newtonian embodimentsherein can be designed to have no or reduced attenuation such that allacoustic acuity is preserved below a predetermined sound pressure level(such as 75 dB). Furthermore, the behavior of a product incorporatingnon-Newtonian fluids can be designed to be instantaneous such thatattenuation occurs immediately once a certain sound pressure level(shearing force) reaches the exposed material. The non-Newtonian fluidscan also be designed such that the exposed material can then immediatelybecome flaccid once the sound pressure level drops below a certain soundpressure level. In yet other embodiments, the non-Newtonian fluids canbe designed or configured or combined with other materials to exhibit adelayed transition to a flaccid state after hardening or exhibit adelayed transition to a hardened state after being in a flaccid state.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasized,according to common practice, that various features of the drawings maynot be drawn to scale. On the contrary, the dimensions of the variousfeatures may be arbitrarily expanded or reduced for clarity. Moreover,in the drawing, common numerical references are used to represent likefeatures. Included in the drawing are the following figures:

FIG. 1 is a cross section diagram of an ear illustrating a generalphysiology of the ear;

FIG. 2A is a cross section diagram of an exemplary earpiece deviceinserted in an ear canal, according to an embodiment of the presentinvention and FIG. 2B is a similar earpiece in a different form factor;

FIG. 3 is a cross section diagram of a portion of the earpiece deviceshown in FIG. 2, according to an embodiment of the present invention;

FIGS. 4A and 4B are respective perspective view and cross sectiondiagrams of an exemplary earpiece device in an expanded state, accordingto another embodiment of the present invention;

FIGS. 4C and 4D are respective perspective view and cross sectiondiagrams of the earpiece device shown in FIGS. 4A and 4B in a contractedstate;

FIG. 5A is a cross section diagram of an exemplary expandable element ina tube illustrating a change in static pressure, according to anembodiment of the present invention;

FIG. 5B is graph of volume as a function of pressure difference for theexpandable element shown in FIG. 5A;

FIG. 6A is a cross section diagram of an exemplary acoustical system,according to an embodiment of the present invention and FIG. 6B is anelectro-acoustical circuit diagram representing the acoustical systemshown in FIG. 6A, according to an embodiment of the present invention;

FIG. 7 is a graph of transmission as a function of frequency for theelectro-acoustic circuit diagram shown in FIG. 6B, for variouscapacitance values of an expandable element;

FIG. 8A is a cross section diagram of an exemplary acoustical system,according to another embodiment of the present invention and FIG. 8B isan electro-acoustical circuit diagram representing the acoustical systemshown in FIG. 8A, according to an embodiment of the present invention;

FIG. 9 is a graph of transmission as a function of frequency for theelectro-acoustic circuit diagram shown in FIG. 8B, for variouscapacitance values of expandable elements;

FIG. 10A is a cross section diagram of an exemplary acoustical system,according to another embodiment of the present invention and FIG. 10B isan electro-acoustical circuit diagram representing the acoustical systemshown in FIG. 10A, according to an embodiment of the present invention

FIG. 11 is a graph of transmission as a function of frequency for theelectro-acoustic circuit diagram shown in FIG. 10B, for various leaksizes between expandable elements;

FIG. 12A is a cross section diagram of an exemplary acoustical system,according to another embodiment of the present invention, FIG. 12B is acircuit diagram of a transfer network associated with the acousticalsystem shown in FIG. 12A, and FIG. 12C is an electro-acoustical circuitdiagram representing the acoustical system shown in FIG. 12A, accordingto an embodiment of the present invention; and

FIG. 13 is a graph of transmission as a function of frequency for theelectro-acoustic circuit diagram shown in FIG. 12C, for variouscapacitance values of an expandable element.

DETAILED DESCRIPTION OF THE INVENTION

Aspects of the present embodiments include methods and devices foroccluding an ear canal which provide a predetermined sound attenuationcharacteristic over various parameters. For example, the predeterminedsound attenuation characteristic can be over a sound pressure levelimpinging on a surface of an occluding member such as a ballooncontaining (or incorporating) non-Newtonian fluid or a member that isjust made of the non-Newtonian fluid. Using the non-Newtonian fluid, theattenuation characteristic will likely provide for greater attenuationas the sound pressure level (SPL) in an ambient field that impinges onthe exterior surface of the non-Newtonian fluid. If the non-Newtonianfluid is a shear thickening fluid (STF), the higher SPL or higher volumewould cause the STF to become more viscous and harder, thereby providinggreater sound attenuation properties in the material itself as a soundgets louder. In other words, as the sound volume exposure to thematerial increases, the greater sound attenuating properties thematerial (made of STFs) will provide as a result of the shear thickeningeffect that STFs provide. Normally, this is considered a benefit forreducing penetration by ballistic weapons such as bullets or for knives,but STFs and non-Newtonian fluids further provide the acoustic benefitof sound attenuation. Of particular benefit is the increased attenuationprovided as the volume or SPL exposure becomes greater. The STFs mayalso provide predetermined attenuation characteristics over otherparameters such as over a frequency band, such that sound is attenuatedmore in one frequency range than in another frequency range of thefrequency band. Exemplary earpiece devices of the present embodimentsinclude an occlusion section or member that can be part of an earpiece.The Occlusion member can be a balloon or expandable member filled withnon-Newtonian fluid or STFs or the occlusion member can just be anon-Newtonian fluid itself. In one embodiment, it can be composed ofmaterial similar to “Silly Putty”™ by Crayola, LLC. Silly Putty is basedon silicone polymers that have unusual physical properties. It bounces,but breaks when given a sharp blow and can also flow like a liquid. Itcontains a viscoelastic liquid silicone, a type of non-Newtonian fluid,which makes it act as a viscous liquid over a long time period but as anelastic solid over a short time period. If a balloon or expandableelement is used, it can be configured to receive a medium such as thenon-Newtonian fluid and to expand to contact and conform to the earcanal. The sound attenuation characteristic of the earpiece device maybe selected based on physical parameters of the occlusion member.

Referring to FIG. 1, a cross section diagram of ear 100 is shown, whichillustrates the general physiology of ear 100. An external portion ofear 100 includes pinna 102 and concha 104. An internal portion of ear100 includes ear canal 108 and tympanic membrane 112.

Pinna 102 is a cartilaginous region of ear 100 that focuses acousticinformation from an ambient environment to ear canal 108. Concha 104 isa bowl shaped region in proximity to ear canal opening, indicated bydashed line 106.

Wall 110 (also referred to herein as ear canal wall 110) of ear canal108 forms an acoustic chamber, which terminates with tympanic membrane112. Sound enters ear canal 108 (at dashed line 106) and is subsequentlyreceived by tympanic membrane 112. Tympanic membrane 112 is a flexiblemembrane in the middle ear that couples to components of the inner ear.In general, acoustic information resident in ear canal 108 vibratestympanic membrane 112. The vibration is converted to a signal(corresponding to the acoustic information) that is provided to anauditory nerve.

Ear canal 108 typically includes cartilaginous region 116 (betweendashed lines 106 and 114) and bony region 118 (between dashed line 114and tympanic membrane 112). Cartilaginous region 116 includes a layer ofcartilage underlying the skin layer. Bony region 118 represents an areawhere bone underlies ear canal wall 110. Vibrations may be conductedthrough the bone (in bony region 118), pass through ear canal wall 110,and may be radiated as sound into ear canal 108.

In bony region 118, a skin layer of ear canal wall 110 may be sensitiveto pressure. In general, the skin layer in bony region 118 isapproximately one tenth a thickness of a skin layer in ear cartilaginousregion 116. Thus, in bony region 118, there is little tissue separatingskin from bone. Accordingly, placement of an object (such as an earplug)in bony region 118 can stimulate nerves (due to skin being pressedagainst bone), which can be uncomfortable and even induce significantpain.

In contrast to bony region 118, cartilaginous region 116 is a highlyflexible region having no substantial rigid structure. Thus,cartilaginous region 116 may be more easily deformed when a force isapplied ear canal wall 110 (in cartilaginous region 116). In general,cartilaginous region 116 is much less sensitive to pressure than bonyregion 118.

In general, application of pressure to ear canal wall 110 (such as by anearplug which occludes ear canal 108), may deform ear canal wall 110.The deformation may, for example, stretch ear canal wall 110 and mayplace the skin layer under tension. Accordingly, it may be desirable toconfigure earpiece devices to be inserted within cartilaginous region116. Earpiece devices may be inserted (and expanded) in cartilaginousregion 116 without inducing discomfort and pain.

In general, ear canal 108 may vary substantially in shape and size overthe human population. In general, ear canal 108 is not straight orregularly shaped. Although not illustrated in FIG. 1, ear canal 108typically includes an upward tilt of approximately 45 degrees, such thattympanic membrane 112 is above the opening (i.e., dashed line 106) ofear canal 108. Ear canal 108 typically includes a first bend near theopening to ear canal 108 and a second bend that is proximate to tympanicmembrane 112.

Because the volume, shape, and length of ear canal 108 may substantiallyvary, there has been difficulty in providing a system that mayeffectively seal ear 100, attenuate noise, mitigate the occlusioneffect, operate under different environmental conditions, and may fit amajority of the population. For example, hearing aid manufacturerstypically generate a full custom earpiece for individuals that include amold of the patient's ear canal. The ear canal mold is then used to forma hearing aid housing. The procedure to create an ear canal mold iscostly, cumbersome, and is not easily adaptable for high volumeproduction. A earpiece and more particularly an occluding member of theearpiece made of a non-Newtonian fluid can be molded and customized fora particular user's ear canal and most likely by the user themselves bythe mere process of insertion of the occluding member into the earcanal.

Referring next to FIG. 2A, a cross section diagram of an exemplaryearpiece device 200 is shown. Earpiece device 200 is shown relative toear 100. Earpiece device 200 may include occlusion member or section 202and housing unit 204 coupled to occlusion section 202. Occlusion section202 may be configured to be inserted in ear canal 108, at a locationbetween the entrance to the ear canal 108 and tympanic membrane 112. Asdiscussed above, it may be desirable to position occlusion section 202within cartilaginous region 116 (FIG. 1) of ear canal 108. Housing unit204 may be positioned outside of ear canal 108. In FIG. 2A, housing unit204 is illustrated as being disposed in ear 100. It is understood thathousing unit 204 may also be configured to be placed behind ear 100 ormay be placed partially behind ear 100 and partially in ear 100.

Occlusion section 202 may include insertion element 206 and expandableelement 208. The expandable element 208 can be a balloon containing anon-Newtonian fluid, but alternatively it can be a material that is justa non-Newtonian fluid without the use of a balloon. Insertion element206 may be coupled to expandable element 208 and may be used to positionexpandable element 208 in ear canal 108. Expandable element 208 isconfigured to be expanded or manipulated in shape, via medium 228.Again, the medium 228 can be a non-Newtonian fluid. In general,expandable element 208 may be configured to form an acoustic seal with aportion of ear canal wall 110. Expandable element 208 may be configuredto partially or fully occlude ear canal 108, to provide various degreesof acoustic isolation (i.e., attenuation of one or more frequencies ofambient sound) at tympanic membrane 112. Furthermore, with the use of anon-Newtonian fluid, the attenuation characteristic can have increasedattenuation as the surface of the element 208 is exposed to greatersound pressure levels (SPL) or volume of sound. In the case of shearthickening fluids, the greater the SPL exposure that the element 208 isexposed to, the greater shear thickening and viscosity the material ofelement 208 will exhibit. Correspondingly, the greater viscosity willprovide greater attenuation characteristics to element 208. As theambient sound increases, the greater attenuation element 208 willexhibit. As the ambient sound subsides or decreases, the lessattenuation element 208 will exhibit. The non-Newtonian essentiallyoperates as a dynamic attenuation device that is passive. In someembodiments, an active component can be added or substituted to providea user greater control of the attenuation characteristics. For example,if the non-Newtonian fluid comprises electrorheological fluids composedof dispersions of electrically polarizable particles in an insulatingfluid, an exposure of the non-Newtonian fluid to an electric fieldcontrols the shear viscosity (and hence attenuation characteristics) ofthe non-Newtonian fluid. Typically a non-Newtonian fluid such aselectrorheological fluids increases in shear viscosity when exposed toan electric field. Alternatively, the non-Newtonian fluid can also bemagnetorheological fluids composed of dispersions of magnetic particlesin an inert or non-magnetic carrier liquid that increases in shearviscosity when exposed to a magnetic field. Thus, controlling themagnetic field about the magnetorheological fluids controls a level ofthe attenuation characteristic of the element containing thenon-Newtonian fluid.

In operation, expandable element 208 may be inserted in ear canal 108 ina contracted state or in a shape that would generally have a smallerdiameter than the orifice of the ear canal. After insertion, expandableelement 208 may be subsequently expanded (e.g., by being filled withmedium 228) or manipulated by squeezing, or pinching, such thatexpandable element 208 conforms to ear canal 108 and forms at least apartial acoustic seal with ear canal 108. To remove earpiece device 200,expandable element 208 may be manipulated again or contracted (e.g., byremoving at least part of medium 228 or manipulating part of the mediumtowards an external surface) back to the contracted state. Accordingly,earpiece device 200 may then be easily removed from ear canal 108.

Expandable element 208 may be formed from any compliant material thathas a low permeability to medium 228. Examples of materials ofexpandable element 208 include any suitable elastomeric material, suchas, without being limited to, silicone, rubber (including syntheticrubber) and polyurethane elastomers (such as Pellethane® andSantoprene™). Materials of expandable element 208 may be used incombination with a barrier layer (for example, a barrier film such asSARANEX™) to reduce the permeability of expandable element 208. Ingeneral, expandable element may be formed from any suitable materialhaving a range of Shore A hardness between about 5 A and about 30 A,with an elongation of about 500% or greater.

Medium 228 may include any suitable liquid, gas or gel capable ofexpanding and contracting expandable element 208 and that would maintaina comfortable level of pressure for a user of earpiece device 200.Examples of medium 228 include, for example, silicone, non or lowpermeable-based polymers, gels, fully-fluorinated liquids, ethyleneglycol, isopropyl alcohol, air or other gasses (for example sulfurhexafluoride (SF6) or hydrogen). In particular embodiments emphasizedherein, the medium can include non-Newtonian fluids such as shearthickening fluids and or fluids as described above.

Insertion element 206 may be formed from, for example, thermoplasticelastomer (TPE) materials, materials having an elastomeric property(such as silicone), or other malleable materials capable of conformingto the ear canal. Expandable element 208 may be attached to insertionelement 206 via any suitable attachment method, such as, but not limitedto, bonding, adherence with an adhesive, thermal bonding, molding andultrasonic bonding.

Although expandable element 208 is illustrated as being of anannular-disc shape, it is understood that expandable element 208 may beformed of other shapes, such as conical-shaped, or toroidal-shaped.Although FIG. 2A illustrates a single expandable element 208, occlusionsection 202 may include multiple co-located expandable elements 208(such as an inner expandable element in an outer expandable element,where each expandable element 208 may be filled with different mediums228). Although FIG. 2A illustrates a single expandable element 208, itis understood that occlusion section 202 may include more than oneexpandable element 208 (for example, as shown in FIG. 8A), where eachexpandable element 208 may be filled with a same medium 228 or withdifferent mediums 228. As noted previously, the expandable element 208can include a balloon, but in some embodiments, the non-Newtonian fluiditself can form the element 208 without the use of a balloon or otherexterior element. For example, in FIG. 2B, the earpiece 200 can have anoccluding member 208A (similar to expandable element 208 of FIG. 2A)that is either made of a non-Newtonian fluid (such as a material like“Silly Putty” described above or non-Newtonian fluids that are capableof being self contained) or comprised of a balloon which has or enclosesa medium comprising the non-Newtonian fluid. The earpiece can include aflange 299 that can cover the orifice of the ear but is not intended tocompletely seal the ear as the balloon is designed for such purposefurther into the external auditory canal (EAC). In one embodiment, theflange can also be made of a non-Newtonian fluid. Further note that theembodiments herein are not limited to earpieces, but can include alltypes of headphones and headsets. In the case of headphones,particularly circum aural headphones that are configured to cover auser's ears can have various portions made of or incorporatenon-Newtonian fluids. For example, the foam padding that typicallycontacts a user's ears can be alternatively made with non-Newtonianfluids or with composites with polyurethane or other alternativematerials. The exterior housing of such headphones can also include orbe made of non-Newtonian fluids or composites (with microfibers, forexample) to provide additional sound attenuation

As described further below with respect to FIGS. 5-13, physicalparameters of occlusion section 202 may be selected to provide apredetermined sound attenuation characteristic over a frequency band orover ambient SPL levels. For example, a compliance of expandable element208, the type of medium 228 (such as non-Newtonian fluid), as well asthe number of expandable elements 208, may be used to design occlusionsection 202 with a specific sound attenuation characteristic (such as ahigh pass filter or a low pass filter) or a dynamic attenuating filterbased on the level of amplitude of an ambient SPL. According to anembodiment of the present invention, a selection of a material for themedium or a selection of particles in a non-Newtonian fluid or otherparameters such as an amount of expansion pressure (of medium 228) withwhich expandable element 208 is expanded may also be selected to controlthe amount of overall sound attenuation, as well as the amount ofocclusion, over the frequency band.

For example, sleep apnea is an example of a noisy environment that canhave an impact on the health of the listener. Because snoring typicallyhas a large portion of its power in the lower frequencies in theacoustic range, a listener subjected to snoring could benefit from ahigh pass filter earpiece that allows higher frequencies of the acousticsignal to be transmitted through the earpiece, while attenuating thelower frequencies. In the case of non-Newtonian fluids, concentration ofparticles, particle size, and particle shape can all play a roll inconfiguring and optimizing an occluding element that can attenuatefrequencies associated with snoring (or other sources of undesirednoise). Other factors that can be used to configure attenuationcharacteristics can include the specific gravity of the fluid used forthe non-Newtonian fluid and the density of the particles, fibers,microparticles or microfibers used for the non-Newtonian fluid. Notethat the term “particles” as used herein is intended to be interpretedin a broad sense to include all types of objects that can be used in anon-Newtonian fluid such as spheres, microspheres, fibers, microfibers,or microparticles. In some embodiments, the specific gravity of thefluid is made to match the density of the particles. Furthermore, thelocation or placement of the non-Newtonian fluid within a device can bevaried and the composition of the non-Newtonian fluid can be varied toprovide specific attenuation profiles. In other words, the fluid can becustomized or designed to have variable compression and decompression orrecovery times. As the non-Newtonian fluid hardens or forms clumps undershear forces, the amount of time that the non-Newtonian fluidrecuperates or returns to a non-clumped or softened state can also be afactor in its attenuation characteristics. Furthermore, the variousvariables above can also be selectively manipulated to design a materialor composite material that exhibits the shear thickening and attenuationcharacteristics that begins to manifest at a particular threshold soundpressure level. Non-Newtonian fluids introduces a entire host ofadditional variables for designing acoustic products (and non-acousticproducts that still utilize acoustics in some form) that can benefitfrom customized attenuation characteristics or parameters not previouslyavailable before.

Housing unit 204 may include inflation management system 210 forcontrolling the transfer of medium 228 to and from occlusion section202, for expanding and contracting expandable element 208. Housing unit204 may also include user interface 212 coupled to inflation managementsystem 210. Inflation management system 210 may be activated responsiveto user interface 212, in order to expand and contract expandableelement 208. Housing unit 204 may also include further electricalcomponents. Inflation management system may include any suitable systemcapable of transferring medium 228 to and from expandable element 208.For example, inflation management system may include a pump actuator anda valve housing (not shown). In some embodiments, no inflationmanagement system would be used. For example, a system usingnon-Newtonian fluid can operate by allowing the user to apply pressureto the element 208 itself to manipulate the shape of the element 208 forinsertion and removal from the ear canal.

According to one embodiment, earpiece device 200 may include inflationmanagement system 210 and user interface 212, without anyelectro-acoustic elements. In this example embodiment, earpiece device200 may be configured simply as a sound isolation device, with apredetermined sound attenuation characteristic selected according to thephysical parameters of occlusion section 202. In another embodiment,the, earpiece device 200 may be without an inflation management system210 as described above.

According to another embodiment, housing unit 204 may include electricalcomponents as well as one or more electro-acoustical components. Forexample, housing unit 204 may include speaker 214, controller 220,memory 222, battery 224 and communication unit 226.

Speaker 214, memory 222, communication unit 226, user interface 212 andinflation management system 210 may be controlled by controller 220.Controller 220 may include, for example, a logic circuit, a digitalsignal processor or a microprocessor.

Communication unit 226 may be configured to receive and/or transmitsignals to earpiece device 200. Communication unit 226 may be configuredfor wired and/or wireless communication with an external device (e.g.,an MPEG player or a mobile phone).

Battery 224 may power the electrical and electro-acoustic components inhousing unit 204. Battery 224 may include a rechargeable or replaceablebattery.

The acoustic seal provided by occlusion section 202 may significantlyreduce a sound pressure level at tympanic membrane 112 from an ambientsound field at the entrance to ear canal 108 (to provide soundisolation). For example, occlusion section 202 having a high pass filtercharacteristic may substantially attenuate lower frequencies. Because ofthe sound isolation of occlusion section 202, speaker 214 may generate afull range bass response time when reproducing sound in earpiece device200.

According to another embodiment, housing unit 204 may include an earcanal (EC) microphone 216 located adjacent to speaker 214, which mayalso be acoustically coupled to ear canal 108. EC microphone 216 may beconfigured to measure a sound pressure level in ear canal 108. The soundpressure level in ear canal 108 may be used, for example, to test thehearing acuity of a user, to confirm an integrity of the acoustic seal,and/or to confirm the operation of EC microphone 216 and speaker 214.Further note that the ear canal microphone can be located in otherlocations than shown, for example, the ear canal microphone 216 can belocated on the other side of the insertion element 206 residing wellwithin the ear canal in some embodiments. The wiring for the ear canalmicrophone 216 in such instance can be fed through the insertion element206 which can be a tube or channel that goes through the element 208.

According to another embodiment, housing unit 204 may include ambientmicrophone 218, as well as EC microphone 216 and speaker 214. Ambientmicrophone 218 may be configured to monitor a sound pressure of theambient environment at the entrance to ear 100. In at least oneexemplary embodiment, earpiece device 200 may actively monitor a soundpressure level both inside and outside ear canal 108 and may enhancespatial and timbral sound quality, while maintaining supervision toensure safe sound reproduction levels. Earpiece device 200, in variousembodiments may conduct listening tests, filter sounds in theenvironment, monitor sounds in the environment, present notificationbased on the monitored sounds, maintain constant audio content toambient sound levels, and/or filter sound in accordance with apersonalized hearing level.

Earpiece device 200 may be configured to generate an ear canal transferfunction (ECTF) to model ear canal 108 (via speaker 214 and ECmicrophone 216), as well as an outer ear canal transfer function (OETF)(via ambient microphone 218). Earpiece device 200 may be configured todetermine a sealing profile with ear 100 to compensate for any acousticleakage. Earpiece device 200 may be configured to monitor a soundexposure to ear canal 108 (for example, from speaker 214 as well as fromambient noise measured via ambient microphone 218).

Referring to FIG. 3, a cross section diagram of earpiece device 200 isshown, which illustrates further components of insertion element 206. InFIG. 3, only some of the components of housing unit 204 are shown, forconvenience. According to an exemplary embodiment, insertion element 206may include pneumatic channel 302. Pneumatic channel 302 may be coupledto expandable element 208 and to inflation management system 210.Pneumatic channel 302 may be used to transfer medium 228 (illustrated bydouble headed arrow A) to and from expandable element 208 via port 308.

In at least one exemplary embodiment, insertion element 206 may includeat least one acoustic channel (e.g., acoustic channel 304 and/oracoustic channel 306) for receiving or delivering audio content. Forexample, housing unit 204 may include speaker 214. Insertion element 206may, thus, include acoustic channel 304 for delivering sound fromspeaker 214 to ear canal 108. As another example, housing unit 204 mayinclude speaker 214 and EC microphone 216. In this example, insertionelement 206 may include acoustic channels 304, 306, respectively coupledto speaker 214 and EC microphone 216. Acoustic channel 306 may deliversound from ear canal 108 to EC microphone 216.

As described above, expandable element 208 may form an acoustic sealwith ear canal wall 110 at a location between the entrance (the orifice)to ear canal 108 and tympanic membrane 112. The acoustic seal byexpandable element 208 may substantially attenuate sound in ear canal108 from the ambient environment (thus providing sound isolation to earcanal 108). Insertion element 206 may also include one or more acousticchannels (e.g., acoustic channel 304 and/or acoustic channel 306) foracoustically coupling sound between ear canal 108 and one or morerespective transducers (e.g., speaker 214 and/or EC microphone 216).Accordingly, sound transmitted to and/or from ear canal 108 via acousticchannel 304 (and/or 306) may be substantially isolated from the ambientenvironment.

Referring next to FIGS. 4A-4D, exemplary earpiece device 200′ is shown.In particular, FIG. 4A is a perspective view diagram of earpiece device200′ with expandable element 208 in an expanded state; FIG. 4B is across section diagram of earpiece device 200′ with expandable element208 in the expanded state: FIG. 4C is a perspective view diagram ofearpiece device 200′ with expandable element 208 in a contracted state;and FIG. 4D is a cross-section diagram of earpiece device 200′ withexpandable element 208 in the contracted state.

Earpiece device 200′ is similar to earpiece device 200 except thatearpiece device 200′ includes flange 402 coupled to insertion element206 of occlusion section 202. Flange 402 may provide sound attenuation(in addition to the sound attenuation by expandable element 208). Flange402 may also help to seat occlusion section 202 in ear canal 108 (FIG.2). Flange 402 may be formed of materials similar to expandable element208.

The selection of physical parameters of occlusion section 202 (FIG. 2)to provide predetermined sound attenuation characteristics is describedbelow.

It is often possible and convenient to represent an acoustical systemwith a lumped element model, as an acoustical circuit analogous to anelectrical circuit. For example, an acoustical system may be representedas an acoustic impedance (or acoustic mobility). In acoustic impedanceanalogs, for example, the sound pressure and volume velocity correspondto voltage and current, respectively. For example, occlusion section 202(FIG. 2) in ear canal 108 may be modeled by an acoustical impedancecircuit.

Referring to FIGS. 5A and 5B, an equivalent acoustical elementrepresentation of balloon 502 (an example of an expandable element)filled with medium 510 in tube 504 is described. In particular, FIG. 5Ais a cross section diagram of balloon 502 in tube 504; and FIG. 5B is anexample of a volume of one face of balloon 502 (for example, face 508)with pressure difference.

Balloon 502 and medium 510 may each be represented as acousticalelements. Because balloon 502 is within tube 504, the band of balloonmaterial in contact with tube walls 506 does not move. This effectivelyseparates balloon 502 into two parts, upstream face 508 and downstreamface 512. It is understood that the acoustical element representation ofdownstream face 512 is the same as that of upstream face 508. Thus, onlyupstream face 508 is considered below.

Face 508 of balloon 502 (filled with medium 510) includes a static DCpressure P₂ on the outside and a static interior pressure P_(g). If theoutside pressure is changed to P₂′, there will be a change in the staticequilibrium of the balloon. Face 508 moves to a new position and mayhave a different shape (represented as face 508′), sweeping out a volumeΔV. Thus, the interior pressure will change to a new value P_(g)′. Theshape of the balloon face 508 is controlled by the difference inpressure across the material, i.e., P_(D)=P₂−P_(g) andP_(D)′=P₂′−P_(g)′.

Although, in general, the relationship between the change in pressuresand the volume of balloon 502 may be complicated, for the acousticalbehavior, it is assumed that these changes are very small, so that asimple acoustical representation of balloon 502 may be determined.

FIG. 5B illustrates an example of the volume change of face 508 ofballoon 502 with a change in pressure difference across the material.Over a small change in pressure difference ΔP_(D), the curve is verynearly linear and the volume change ΔV may be represented as:

$\begin{matrix}{{\Delta V} \approx {\left( \frac{\partial V}{\partial P_{D}} \right)_{P_{D}}\Delta\; P_{D}} \equiv {C_{2}\Delta\;{P_{D}.}}} & (1)\end{matrix}$

For acoustic pressures, the pressures acting on face 508 may beconsidered to oscillate sinusoidally in time about their static values,and may be represented by complex notation as

P ₂ ′=P ₂+Re{p ₂ e ^(iωt)}  (2)

P _(g) ′=P _(g)+Re{p _(g) e ^(iωt)}  (3)

where p_(g) and p₂ are the (complex) sound pressures on either side ofthe balloon section, so that

ΔP _(D)=Re{(P ₂ −p _(g))e ^(iωt)}.  (4)

Similarly, the volume changes harmonically as

ΔV=V′−V=Re{V*e ^(iωt)}  (5)

where V is the static volume enclosed by face 508 of the balloon. Thus,the volume velocity U (i.e., the rate change of volume with time) may berepresented as

$\begin{matrix}{{U \equiv {{Re}\left\{ {u_{2}e^{i\;\omega\; f}} \right\}}} = {\frac{{dV}^{\prime}}{dt} = {{Re}{\left\{ {i\omega V^{*}e^{i\;\omega\; f}} \right\}.}}}} & (6)\end{matrix}$

Accordingly, the sound pressure difference is related to the complexvolume velocity u₂, as

$\begin{matrix}{{p_{2} - p_{g}} = \frac{u_{2}}{i\omega C_{2}}} & (7)\end{matrix}$

where C₂ is the acoustical capacitance of one side (for example face508) of balloon 502. The value of capacitance C₂ may be determined bythe slope of the tangent line in FIG. 5B.

Medium 510 may include, for example, a gas or a liquid. The acousticalelement representation of medium 510 may be different depending onwhether medium 510 is a gas or a liquid. The consideration of medium 510as a liquid is discussed with respect to FIG. 12. The acousticalrepresentation of medium 510 that includes a gas is considered below.Accordingly, medium 510 is referred to below as gas 510.

An enclosed volume of gas may store energy in its compressions. Thus,gas 510 (for example, air) within balloon 502 may also be represented asan acoustic capacitance. The volume velocity u₂, as defined, acts tocompress gas 510 contained within balloon 502. The volume velocitycorresponding to face 512 of balloon 502 may be defined in the oppositesense, such that the volume velocity u₁ acts to uncompress the air. Thenet volume velocity (u₂-u₁) is related to the sound pressure p_(g)inside the balloon by:

u ₂ −u ₁ =iωC _(g) p _(g)  (8)

where capacitance C_(g) is given by:

$\begin{matrix}{C_{g} = \frac{V_{g}}{\gamma\; P_{g}}} & (9)\end{matrix}$

and where V_(g) is the enclosed volume, P_(g) is the static pressureinside balloon 502, and γ is the specific heat ratio.

Referring to FIGS. 6A and 6B, acoustical system 600 representing anexpandable element in an ear canal is shown. In particular, FIG. 6A is across section diagram of acoustical system 600 including balloon 502 intube 504 having anechoic termination 602; and FIG. 6B is anelectro-acoustical circuit diagram of acoustical system 600. Acousticalsystem 600 represents an expandable element (balloon 502) in an earcanal (tube 504) having a tympanic membrane (anechoic termination 602).Although not illustrated, balloon 502 may be formed on an insertionelement (such as insertion element 206 shown in FIG. 2).

If the lateral dimensions of tube 504 are less than a wavelength ofsound, sound waves may propagate along both forward and backwardlongitudinal directions. Because tube 504 includes anechoic termination602, there are no reflected sound waves, only forward propagating waves.

Consider pressure P₁ and volume velocity u₁ at a position in tube 504.For a plane wave traveling in a single direction, the pressure and thevolume velocity are in phase and are related as:

P ₁ =R _(c) u ₁  (10)

where the characteristic acoustical resistance of tube 504 (at anechoictermination 602) is

$\begin{matrix}{{R_{c} = \frac{\rho c}{A}}.} & (11)\end{matrix}$

Here, A is the internal cross-sectional area of tube 504, p is thedensity of the gas (e.g., air), and c is the sound speed in the gas(e.g., air).

As discussed above, faces 508, 512 of balloon 502 may each berepresented as acoustical compliance C_(b). Gas 510 within balloon 502may be represented as acoustical compliance C_(g). Finally, tube 504with anechoic termination 602 may be represented as resistance R_(c).

Based on the acoustical elements representing balloon 502, gas 510 andtube 504, acoustical system 600 may be represented as an equivalentelectro-acoustical circuit (i.e., an acoustical impedance analog), asshown in FIG. 6B. Thus capacitance C_(b) of face 508 receives pressurep₂. Capacitance C_(b) is coupled to capacitance C_(g) of gas 510 andcapacitance C_(b) of face 512. Capacitance C_(b) of face 512 is coupledto resistance R_(c) of the termination of tube 504. Thus, pressure p₂ isprovided at an output terminal of the circuit. It is understood that theelectro-acoustic circuit may be modified to account for the finite sizeof insertion element 206 (FIG. 2) on which balloon 502 may be mounted.

Network methods may be applied to calculate the various quantities ofthe acoustical elements if values for the various circuit elements areavailable. Both R_(c) and C_(b) may be determined from the expressionsprovided above.

For a sample calculation, it is assumed that tube 504 has an innerdiameter of 9.53 mm (0.375″) and that balloon 502 contains a volume of0.713 cm³ at an inflation pressure of 300 mbar. Capacitance C_(b)corresponding to each face of balloon 502 may be determined, forexample, based on a calculation of the inflation dynamics of balloonmaterials, taking into account the Mooney-Rivlin type of stress-strainrelationship. In the sample calculation, several different values ofcapacitance including C_(b)=0.3C_(g), C_(b)=C_(g), and C_(b)=3 C_(g) areselected. The transmission coefficient of acoustical energy may bedetermined as:

$\begin{matrix}{T = {20\mspace{14mu}\log{{\frac{p_{1}}{p_{2}}}.}}} & (12)\end{matrix}$

Referring to FIG. 7, the calculated transmission coefficients for thesethree values of capacitance C_(b) are shown. Curves 702, 704 and 706represent capacitance values C_(b)=3 C_(g), C_(b)=C_(g) andC_(b)=0.3C_(g), respectively. All curves show about a 6 decibel (dB) peroctave drop off at the lower frequencies. Accordingly, balloon 502 actsas a first order high-pass filter.

Referring next to FIGS. 8A and 8B, acoustical system 800 is shown, whichrepresents two expandable elements in an ear canal. In particular, FIG.8A is a cross section diagram of acoustical system 800 includingballoons 802-A, 802-B in tube 504 having anechoic termination 602; andFIG. 8B is an electro-acoustical circuit diagram of acoustical system800. Balloons 802-A, 802-B are filled with gas 808-A, 808-B.

Acoustical system 800 is similar to acoustical system 600 (FIGS. 6A and6B), except that acoustical system 800 includes two balloons 802-A,802-B (i.e., two expandable elements), and balloons 802-A, 802-B areillustrated as being mounted on insertion element 804. Two balloons802-A, 802-B may be formed, for example, from a single balloon materialattached to insertion element 804 at attachment points 805 and 806. Inan exemplary embodiment, attachment point 806 represents an O-ringapproximately midway along a length of a single balloon. As anotherexample, balloons 802-A, 802-B may be formed from different balloonmaterials attached at respective attachment points 805, 806. Gas 808-Bmay be the same as gas 808-A or may be different from gas 808-A.

Balloons 802-A, 802-B have respective volumes of V_(A) and V_(B), withrespective sound pressures of p_(A) and p_(B). Gap 810 between balloons802-A, 802-B (at attachment point 806) has volume V_(c) and soundpressure p_(c). The motion of the right-hand face of balloon 802-Aincludes a volume velocity u_(A). Similarly, the motion of the left-handface of balloon 802-B includes a volume velocity u_(B).

Based on the acoustical elements described above for balloon 502 (FIGS.6A and 6B), gas 510 and tube 504, acoustical system 800 may also berepresented as an equivalent electro-acoustical circuit (i.e., anacoustical impedance analog), as shown in FIG. 8B. Thus, capacitancesC_(bA1), C_(gA), C_(bA2) are associated with the left face of balloon802-A, gas 808-A and the right face of balloon 802-A, respectively.Capacitance C_(c) is associated with gap 810. Capacitances C_(bB1),C_(gB), C_(bB2) are associated with the left face of balloon 802-B, gas808-B and the right face of balloon 802-B, respectively. Although notshown, it is understood that the electro-acoustic circuit shown in FIG.8B may be modified to account for insertion element 804.

Referring to FIG. 9, example transmission coefficients are shown for theelectro-acoustical circuit shown in FIG. 8B, using several differentvalues of capacitance. In this example, both balloons 802-A, 802-B havea volume of 0.222 cm³ and an inflation pressure of 300 mbar, so thatC_(gA)=C_(gB). Gap 810 between balloons 802-A, 802-B is at atmosphericpressure and has a volume of 0.095 cm³. Three different selections ofballoon capacitances are used. For curve 902, the capacitances areC_(bA1)=C_(bA2)=C_(bB1)=C_(bB2)=3C_(gA). For curve 904, the capacitancesare C_(bA1)=C_(bB1)=3C_(gA) and C_(bA2)=C_(bB2)=C_(gA). For curve 904,the capacitances are C_(bA1)=C_(bA2)=C_(bB1)=C_(bB2)=C_(gA).

As shown in FIG. 9, the acoustical transmission for two balloons 802-A,802-B is similar to the acoustical transmission of a single balloon(shown in FIG. 7). Thus, similar to the single balloon (FIG. 7), thecombination of two balloons 802-A, 802-B also acts like a first-orderhigh-pass filter, with approximately a 6 dB/octave slope at lowfrequencies.

FIG. 8A illustrates acoustical system 800 including two balloons 802-A,802-B disposed along a length of insertion element 804 (i.e., in seriesarrangement, as illustrated in FIG. 8B). According to anotherembodiment, balloons 802-A, 802-B may be co-located on insertion element804. Balloons 802-A, 802-B, thus, may be formed in a parallelarrangement.

Measurements on several double balloons, however, have revealed a morecomplicated variation with frequency. This variation may be due to smallleaks between balloons 802-A, 802-B.

Referring next to FIGS. 10A and 10B, acoustical system 1000 is shown,which represents two expandable elements in an ear canal. In particular,FIG. 10A is a cross section diagram of acoustical system 1000 includingballoons 802-A, 802-B in tube 504 having anechoic termination 602; andFIG. 10B is an electro-acoustical circuit diagram of acoustical system1000. Acoustical system 1000 is similar to acoustical system 800 (FIGS.8A and 8B), except that acoustical system 1000 includes leak 1002 atattachment point 806.

Leak 1002 may be modeled as a short, circular passage between balloons802-A, 802-B. The volume velocity entering leak 1002 is represented asu_(LA) and the volume velocity exiting leak 1002 is represented asu_(LB). A volume of fluid (gas or liquid) that has a length comparableor greater than a wavelength (or a radius that is comparable or smallerthan a viscous boundary layer thickness) may not be capable of beingtreated as a simple volume. Accordingly, a general theory is describedbelow for acoustical propagation along a circular passage (i.e., leak1002).

Consider that leak 1002 is a hollow, circular passage of radius a_(L)and length l. At one end of leak 1002, there is a pressure p_(A) andvolume velocity u_(LA); at the other end, there is a pressure p_(B) andvolume velocity u_(LB). These quantities are related, generally, througha transfer matrix T_(L) as:

$\begin{matrix}{{\begin{bmatrix}p_{A} \\u_{LA}\end{bmatrix} = {{T_{L}\begin{bmatrix}p_{B} \\u_{LB}\end{bmatrix}} = {\begin{bmatrix}{\cosh\;\Gamma\; l} & {Z\;\sinh\;\Gamma\; l} \\{Z^{- 1}{si}\; n\; h\;\Gamma\; l} & {\cosh\;\Gamma\; l}\end{bmatrix}\begin{bmatrix}p_{B} \\u_{LB}\end{bmatrix}}}}{where}} & (13) \\{\Gamma = {i\frac{\omega}{c}\sqrt{\frac{T_{\alpha}}{T_{\beta}}}}} & (14) \\{{Z = \frac{\rho c}{\pi\; a_{L}^{2}\sqrt{T_{\alpha}T_{\beta}}}}{with}} & (15) \\{T_{\alpha} = {1 + \frac{2\left( {\gamma - 1} \right){J_{1}\left( {\alpha_{L}\alpha} \right)}}{\alpha_{L}\alpha{J_{0}\left( {\alpha_{L}\alpha} \right)}}}} & (16) \\{T_{\beta} = {1 - \frac{2{J_{1}\left( {a_{L}\beta} \right)}}{a_{L}\beta{J_{0}\left( {a_{L}\beta} \right)}}}} & (17) \\{\alpha = \sqrt{\frac{{- i}\rho\omega N_{pr}}{\mu}}} & (18) \\{\beta = \sqrt{\frac{{- i}\;\rho\;\omega}{\mu}}} & (19)\end{matrix}$

where μ represents the coefficient of viscosity of the gas (e.g., air),γ represents the ratio of specific heats, N_(pr) represents the Prandtlnumber and J₀(*),J₁(*) represent Bessel functions of the first kind forrespective integer orders 0 and 1.

Leak 1002 that is a circular tube, in general, does not have a simplelumped-element representation. However, leak 1002 may be represented asa network block in an electro acoustical circuit. Accordingly, based onthe acoustical elements described above, acoustical system 1000 havingleak 1002 may also be represented as an equivalent electro-acousticalcircuit (i.e., an acoustical impedance analog), as shown in FIG. 10B. InFIG. 10B, network block 1004 with transfer matrix T_(L) represents leak1002. The circuit shown in FIG. 10B is similar to the circuit shown inFIG. 8B, except for the inclusion of network block 1004. Network block1004 may act in parallel to some of the circuit elements representingballoons 802-A, 802-B.

Referring to FIG. 11, example transmission coefficients are shown forthe electro-acoustical circuit shown in FIG. 10B, using severaldifferent leak sizes (and eq. (13) for the transfer matrix T_(L)). Theleak sizes include radii of 0 cm (i.e., no leak), 0.017 cm, 0.05 cm and0.1 cm. In particular, curves 1102, 1104, 1106 and 1108 representrespective leak sizes of 0 cm, 0.017 cm, 0.05 cm, and 0.1 cm. As shownin FIG. 11, there is a transition from one type of behavior to anotherwith leak size. For a large radius leak (curve 1108), acoustical system1000 effectively represents a single large balloon, with a 6 dB/octavedrop at low frequencies. For a zero leak (curve 1102), acoustical system1000 represents a double balloon system, also with a 6 dB/octave lowfrequency behavior. At intermediate sized leaks (curves 1104 and 1106),acoustical system 1000 transitions from a single balloon mode at lowfrequencies to a double balloon mode at high frequencies, thus producinga more complex frequency variation over approximately the 200 Hz-2000 Hzrange. In the example shown in FIG. 11, the attenuation is relativelyflat for the 0.017 cm leak (curve 1104). Accordingly, it may be possibleto design leaks between balloons 802-A, 802-B to selectively shape thetransmission (and attenuation) to a desired response over a range offrequencies.

Referring next to FIGS. 12A-12C, acoustical system 1200 is shown, whichrepresents a liquid-filled expandable element in an ear canal. Inparticular, FIG. 12A is a cross section diagram of acoustical system1200 including balloon 502 filled with liquid 1202 in tube 504 havinganechoic termination 602; FIG. 12B is a circuit diagram of a transfernetwork associated with balloon 502 filled with liquid 1202; and FIG.12C is an electro-acoustical circuit diagram of acoustical system 1200.

Acoustical system 1200 is similar to acoustical system 600 (FIGS. 6A and6B), except that acoustical system 1200 includes balloon 502 filled withliquid 1202. Filling balloon 502 with liquid 1202 (for example, waterinstead of air), may change the acoustical behavior of balloon 502. Ifballoon 502 is of sufficiently short length, it may be treated as asmall volume (similar to holding a volume of gas as described above).For balloon 502 having a length comparable to a wavelength, balloon 502may be treated as a transmission line. This may be the case for liquid1202, because the sound speed in liquids is considerably higher than inair, such that the wavelengths are correspondingly longer. In the caseof non-Newtonian liquids, the sound speeds may vary from conventionalliquids.

The pressure just inside face 508 of balloon 502 is represented as P_(A)and the pressure just inside face 512 is represented as p_(B). Let L bethe length of the balloon and a, the internal diameter of theconstraining tube. The sound pressures (p_(A), p_(B)) and volumevelocities (u₁, u₂) may be related through a transfer matrix T_(liq) by:

$\begin{matrix}{\begin{bmatrix}p_{A} \\u_{2}\end{bmatrix} = {{T_{liq}\begin{bmatrix}p_{B} \\u_{1}\end{bmatrix}} = {\begin{bmatrix}{\cosh\;\Gamma\; L} & {Z\;\sinh\;\Gamma\; L} \\{Z^{- 1}\sinh\;\Gamma\; L} & {\cosh\;\Gamma\; L}\end{bmatrix}\begin{bmatrix}p_{B} \\u_{1}\end{bmatrix}}}} & (20)\end{matrix}$

If a is sufficiently large, viscous and thermal boundary layer effectsmay be ignored, such that the arguments αα and αβ are also large andT_(α)≈T_(β)≈1. Then,

$\begin{matrix}{\begin{bmatrix}p_{A} \\u_{2}\end{bmatrix} \approx {\begin{bmatrix}{\cos\;{kL}} & {iZ_{liq}\sin\;{kL}} \\{{iZ}_{liq}^{- 1}\sin\;{kL}} & {\cos\;{kL}}\end{bmatrix}\begin{bmatrix}p_{B} \\u_{1}\end{bmatrix}}} & (21)\end{matrix}$

where k=ω/c_(liq) is the wavenumber and Z_(liq) is the characteristicimpedance of the liquid, given as

$\begin{matrix}{{Z_{liq} = \frac{\rho_{liq}c_{liq}}{\pi\; a^{2}}}.} & (22)\end{matrix}$

As shown in FIG. 12B, eq. (21) may be represented as a transfer network.For the transfer network:

$\begin{matrix}{{Z_{1} = {Z_{2} = {Z_{3}\left( {{\cos\;{kL}} - 1} \right)}}}{where}} & (23) \\{Z_{3} = \frac{Z_{liq}}{i\;\sin\;{kL}}} & (24)\end{matrix}$

If it is further assumed that kL is small, the expressions simplifyfurther, yielding

$\begin{matrix}{{Z_{1} = {Z_{2} = {i\;\omega\; L_{liq}}}}{where}} & (25) \\{Z_{3} = {\frac{1}{i\;\omega\; C_{liq}}.}} & (26)\end{matrix}$

In eqs. (25) and (26), L_(liq) represents an inductance and C_(liq)represents a capacitance, respectively, where:

$\begin{matrix}{{L_{liq} = \frac{\rho_{liq}L}{\pi\; a^{2}}}{and}} & (27) \\{C_{liq} = {\frac{\pi\; a^{2}L}{\rho_{liq}c_{liq}^{2}}.}} & (28)\end{matrix}$

The inductance L_(liq) is directly related to the mass of the liquidcontained in the volume. The capacitance C_(liq) is related to thecompliance of the liquid.

Accordingly, based on the acoustical elements described above, and thetransfer network shown in FIG. 12B, acoustical system 1200 may berepresented as an equivalent electro-acoustical circuit (i.e., anacoustical impedance analog), as shown in FIG. 12C. The circuit shown inFIG. 12C is similar to the circuit shown in FIG. 6B, except for theinclusion of inductances L_(liq), and the replacement of capacitanceC_(g) with capacitance C_(liq).

Referring to FIG. 13, example transmission coefficients are shown forthe electro-acoustical circuit shown in FIG. 12C, using several valuesof capacitance for a water-filled balloon. For the example, the balloonvolume is 0.713 cm³ and the constraining tube has an inner diameter of0.953 cm. The capacitance C_(b) of faces 508, 512 may be estimatedaccording to the following argument. The shape of balloon 502 oninflation may depend mainly on the pressure difference across themembrane and not on what liquid 1202 (e.g., water) balloon 502 contains.If water-filled balloon 502 is inflated to a volume comparable to thatof an air-filled balloon, there may be a comparable inflation pressure.In the example, the inflation pressure is selected as 300 mbar. Thecapacitances C_(b) include 3C_(g), C_(g), and 0.3C_(g). In particular,curve 1302 represents C_(b)=C_(g), curve 1304 represents C_(b)=0.3C_(g)and curve 1306 represents C_(b)=3C_(g). As shown in FIG. 13, thetransmission is quite low up to about 2 or 3 kHz. Curves 1302 and 1304include a low frequency resonance due to the mass of the water and thestiffness of the balloon material. In general, by filling balloon 502with liquid 1202, system 1200 may act as a low pass filter. Presumablyfilling the balloon 502 with a non-Newtonian liquid (instead of water)will alter the characteristics of the curve in FIG. 13 reflecting evengreater attenuation overall.

Referring generally to FIGS. 2 and 6A-13, exemplary occlusion sections202 of the present invention may be formed to produce a predeterminedsound attenuation characteristic over a frequency band, for an expandedstate of one or more expandable elements 208. The predetermined soundattenuation characteristic may be produced by selecting physicalparameters of occlusion section 202 (such as the material of expandableelement 208, medium 228, as well as the effects of insertion element206) in accordance with an electro-acoustical circuit model of occlusionsection 202 in ear canal 108. Thus, appropriate materials and mediumsmay be selected that substantially match acoustical elementcharacterizations of expandable element 208 and medium 228, to producethe predetermined sound attenuation characteristic. The predeterminedsound attenuation characteristic, in general, may include a firstfrequency range over which sound is substantially attenuated and asecond frequency range over which sound is substantially passed. Use ofdifferent non-Newtonian fluids in terms of size of particles,concentration of particles, shapes of particles, types of mixtures withother materials (such as fibers or with polyurethane to form foam),types of particles (e.g., spheres, rods, nanotubes, fibers, etc.) usedand whether no particles are used will provide even more options incustomizing sound attenuation characteristics unavailable to designerspreviously before.

It is understood that a predetermined sound attenuation characteristicmay also be produced by combining multiple expandable elements 208 (withsimilar or different materials) filled with different mediums 228. Forexample, a first expandable element 208 filled with gas (to produce ahigh pass filter) may be coupled with a second expandable element 208filled with a liquid (to produce a low pass filter). The combination ofthe two expandable elements 208 with different mediums 228 may produce aband pass filter. The combinations of different non-Newtonian fluids ornon-Newtonian fluids in one expandable element and other fluids or gasin a separate expandable element may also provide further options inproviding customized predetermined sound attenuations characteristics.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. An earpiece, comprising: an ambient microphoneconfigured to measure the ambient sound near the entrance to a user'sear canal; an internal microphone configured to measure the sound withinthe user's ear canal; a user interface; a memory that storesinstructions; an expandable element configured to contain a medium; aninflation management system configured to move a medium into and out ofthe expandable element; a controller, wherein the controller isconfigured to execute the instructions to perform operations comprising:receiving an activation signal from the user interface and activatingthe inflation management system; sending a signal to the inflationmanagement system to move medium into the expandable element; andsending a signal to the inflation management system to stop mediummovement when a threshold comfortable pressure level is reached.
 2. Theearpiece according to claim 1, wherein the medium is a non-Newtonianfluid.
 3. The earpiece according to claim 2, wherein the non-Newtonianfluid is at least one of poly vinyl alcohol, poly dimethylsiloxane,electrorheological fluid, magnetorheological fluid, or a combinationthereof.
 4. The earpiece according to claim 1, wherein the mediumincludes a carrier liquid and at least one of particles, microspheres,microfibers, rod-like element, nanoparticles, or nano-tubes or acombination thereof.
 5. The earpiece according to claim 4, wherein thecarrier fluid is at least one of water, ethylene glycol, or acombination thereof.
 6. The earpiece according to claim 4, wherein theparticles include at least one of silica, titanium, oxide, calciumcarbonate, cornstarch, synthetically occurring minerals, naturallyoccurring minerals, polymers, glass, stainless steel or a combinationthereof.
 7. The earpiece according to claim 6, wherein the particles aremagnetic.
 8. The earpiece according to claim 6, wherein the carrierliquid is magnetic.